This application relates to signal oscillators based on photonic devices.
Radio frequency (RF) and microwave oscillators for generating signals in the RF and microwave frequencies are used in a wide range of applications including circuits, communication devices and others. Such RF and microwave oscillators may be constructed as “hybrid” devices by using both electronic and optical components to form opto-electronic oscillators (“OEOs”). See, e.g., U.S. Pat. Nos. 5,723,856, 5,777,778, 5,929,430 and 6,567,436.
For example, such an OEO can include an electrically controllable optical modulator and at least one active opto-electronic feedback loop that includes an optical part and an electrical part interconnected by a photodetector. The opto-electronic feedback loop receives the modulated optical output from the modulator and converted the modulated optical output into an electrical signal which is applied to control the modulator. The feedback loop produces a desired long delay in the optical part of the loop to suppress phase noise and feeds the converted electrical signal in phase to the modulator to generate the optical modulation and generate and sustain an electrical oscillation in RF or microwave frequencies when the total loop gain of the active opto-electronic loop and any other additional feedback loops exceeds the total loss. Such an opto-electronic loop is an active, in-phase loop that oscillates and thus is different from the conventional feedback loop that stabilizes a device at a particular stable operating condition or state. The generated oscillating signals are tunable in frequency and can have narrow spectral linewidths and low phase noise in comparison with the signals produced by other RF and microwaves oscillators.